1. Field of the Invention
The present invention relates to hardening methods and hardening devices, more specifically to a hardening method and a hardening device for hardening a work having a shaft and a hole on a flat plate.
2. Description of the Related Art
Conventionally, a built-up crank is assembled after every component thereof is hardened. Herein, a built-up crank is a crank having a configuration shown in FIGS. 13A and 13B. As shown in FIG. 13A, a part 51, which is one component of a built-up crank 50, has a configuration in which a shaft 54 is unitarily formed in a center of a flat plate (circular plate) 53. The flat plate 53 also has a hole 55, which is formed close to the shaft 54. Further, as shown in FIG. 13B, a pin 52, which is another component, is fixed to the hole 55 by means such as a close fit. The built-up crank 50 is constituted by combining two flat plates 53 of two parts 51 by the common pin 52.
As seen in the part 51 of the crank 50, there is a work (object to be hardened) having a complicated configuration in which a portion (shaft 54) extending from the flat plate 53 and the hole 55 are close to each other. Such an intricately-shaped work has conventionally subjected to hardening onto individual components (the shaft 54 and an inner wall of the hole 55 in this case) by a device such as a hardening device disclosed in a patent document 1 specified below or a helical heating conductive body.    Patent Document 1: JP 2001-115211 A